1. Field of the Invention
The present invention relates generally to a vehicular height control system for an automotive suspension system for adjusting or regulating height level of various portions of a vehicle body and whereby for regulating vehicle body attitude. More specifically, the invention relates to a vehicular height control system which is provided an improved control characteristics during travel through an undulated road and/or rough road which may cause bottoming at one or more suspension systems of the vehicle.
2. Description of the Background Art
Conventionally, various vehicular height regulating or controlling systems have been developed and proposed. These conventional vehicular height control systems are designed for controlling height level of the vehicle body at various portions thereof so that attitude of the vehicle bodies can be regulated at various vehicle driving condition for providing better drivability and riding comfort. For example, one of the typical construction of vehicular height control system has been disclosed in the Japanese Patent First Publication (Tokkai) Showa No. 53-51823. The disclosed vehicular height control system includes a feature of disabling height adjustment in preselected vehicular driving condition, such as during braking and acceleration or deceleration in which vehicular pitching motion is expected and during turning in which vehicular rolling is expected. In this system, it is intended to avoid the system to fall into in acurately height adjusting condition due to abrupt change of vehicular attitude. This system is successful in preventing the vehicular height control system from inacurately controlling the vehicular height in a vehicle condition in which vehicular pitching or rolling motion occurs.
However, the prior proposed system does not concern about the vehicular attitude change due to road surface condition. For instance, on an undulated load or substantially rough road, the vehicular attitude changes due to uneveness of the road surface. When the magnitude of undulation on the road surface is substantial, the vehicle attitude may change substantially to cause vehicular height control operation. However, since vehicular height frequently changes on the undulated or rough road, precise height adjustment cannot be expected. Furthermore, due to frequent change of directions, i.e. rising direction and lowering direction, of height adjustment, the height adjustment tends to be terminated at inaccurate height level. This clearly degrades riding comfort and drivability of the vehicle.